Magnetic resonance imaging apparatus and a method for determining trigger timing of ce-mra scan

ABSTRACT

The present invention discloses an apparatus and a method for determining a trigger timing of a CE-MRA scan. The apparatus comprises: a blood flow velocity acquisition unit configured to acquire a blood flow velocity of a target vessel; and a trigger timing determination unit configured to determine the trigger timing for performing the CE-MAR scan on a CE-MRA scan region according to the blood flow velocity and a predetermined image acquisition condition during a monitoring scan. The apparatus and method take the blood flow velocity into consideration, and can determine the trigger timing of the CE-MRA scan automatically and accurately.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 13/684,418, filed Nov. 23, 2012, which is based upon and claims thebenefit of priority from Chinese Patent Application No. 201110381985.3,filed on Nov. 25, 2011. The entire contents of the above-identifiedapplications are incorporated herein by reference.

FIELD

The present invention relates to the technical field of MagneticResonance Imaging (MRI), and more particularly to an apparatus and amethod for determining a trigger timing of a Contrast Enhanced MagneticResonance Angiography (CE-MRA) scan.

BACKGROUND

CE-MRA is a technique used in the field of MRI. In CE-MRA, a contrastagent (also referred to as angiography agent) is injected to a vessel toenhance the contrast of a nuclear magnetic resonance image to obtain aclear and visual image of the vessel.

Ideally, a CE-MRA scan is triggered (started) when the concentration ofthe contrast agent reaches a peak value in a Region of Interest (ROI).However, in fact, there is a time period from when the CE-MRA scan istriggered to when an image of the ROI is acquired by the CE-MRA scan.

In order to get an optimal trigger timing of the CE-MRA scan, amonitoring scan is performed to observe the flow of the contrast agent.As blood is flowing, a monitoring scan region (also called a monitorregion) is generally arranged with an offset away from a CE-MRA scanregion in the direction of the blood flow, as shown in FIG. 1. Themonitor region is located in the same plane with the CE-MRA scan regionso as to ensure that the monitor region is identical to the scan regionor at least includes a part of the scan region. By arranging the monitorregion to lead the scan region by the offset, an operator of a CE-MRAsystem is allowed to have enough time to trigger the CE-MRA scan whenseeing the contrast agent in a fluoroscopic image (a monitor image)acquired from the monitoring scan.

U.S. Pat. No. 6,489,486B1 discloses a Magnetic Resonance (MR)pre-imaging method. In this U.S. patent application, a monitor region islocated manually. In addition, the operator of an MR system must focuson the continuously-displayed fluoroscopic images so as to observe theflow of the contrast agent and determine a trigger timing for a CE-MRAscan. Therefore, the operator must be experienced.

Several methods have been developed in the prior art to trigger a CE-MRAscan automatically. U.S. Pat. No. 6,167,293A discloses a method forperforming MRA. In this U.S. patent application, a signal value, i.e.the concentration of a contrast agent, in a pre-selected region, i.e. amonitor region, is monitored, and a CE-MRA scan is started automaticallywhen the signal value exceeds a specified threshold value. In thismethod, the monitor region is also manually selected by an operator.Moreover, in this method, the advance or delay of the contrast agentpeak due to the blood flow velocity is not taken into consideration.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be better understood by reference to thefollowing description taken in conjunction with accompanying drawings.In the accompanying drawings, identical or like components aredesignated with identical or like reference signs designate. Theaccompanying drawings, together with the detailed description below, areincorporated into and form a part of the specification, and serve tofurther illustrate, by way of example, preferred embodiments of thepresent invention and to explain the principle and advantages of thepresent invention. In the accompanying drawings:

FIG. 1 is a schematic diagram illustrating a monitor region and a CE-MRAscan region;

FIG. 2 is a schematic flow chart illustrating a method for determining atrigger timing of a CE-MRA scan according to an embodiment of thepresent invention;

FIG. 3 is a schematic diagram illustrating a time period between thetime point when a CE-MRA scan is triggered and the time point when aneffective CE-MRA scan image is acquired;

FIG. 4 is a schematic flow chart illustrating a step of determining atrigger timing according to an embodiment of the present invention;

FIG. 5 is a schematic flow chart illustrating a step of determining atrigger timing according to another embodiment of the present invention;

FIG. 6 is a schematic diagram illustrating a trigger position accordingto an embodiment of the present invention;

FIG. 7a -FIG. 7b are schematic diagrams showing a monitor regioncontaining two target vessels;

FIG. 8a -FIG. 8b are schematic diagrams showing a monitor regioncontaining tree-shaped target vessels;

FIG. 9 is a schematic flow chart illustrating a step of determining amonitor region according to an embodiment of the present invention;

FIG. 10 is a schematic flow chart illustrating a step of determining amonitor region according to another embodiment of the present invention;

FIG. 11 is a schematic block diagram illustrating an apparatus fordetermining a trigger timing of a CE-MRA scan according to an embodimentof the present invention;

FIG. 12 is a schematic block diagram illustrating a blood flow velocityacquisition unit according to an embodiment of the present invention;

FIG. 13 is a schematic block diagram illustrating a trigger timingdetermination unit according to an embodiment of the present invention;

FIG. 14 is a schematic block diagram illustrating a trigger timingdetermination unit according to another embodiment of the presentinvention;

FIG. 15 is a schematic block diagram illustrating a trigger timingdetermination subunit according to an embodiment of the presentinvention;

FIG. 16 is a schematic block diagram illustrating a trigger timingdetermination subunit according to another embodiment of the presentinvention;

FIG. 17 is a schematic block diagram illustrating a trigger timingdetermination subunit according to another embodiment of the presentinvention;

FIG. 18 is a schematic block diagram illustrating a trigger timingdetermination subunit according to another embodiment of the presentinvention;

FIG. 19 is a schematic block diagram illustrating an apparatus fordetermining a trigger timing of a CE-MRA scan according to anotherembodiment of the present invention;

FIG. 20 is a schematic block diagram illustrating a monitor regiondetermination unit according to an embodiment of the present invention;

FIG. 21 is a schematic block diagram illustrating a monitor regiondetermination unit according to another embodiment of the presentinvention;

FIG. 22 is an exemplary block diagram illustrating the structure of acomputer capable of implementing the embodiments/examples of the presentinvention; and

FIG. 23 is a functional block diagram depicting a configuration of anMRI apparatus.

DETAILED DESCRIPTION

The following presents a simplified summary of the present invention toprovide a basic understanding of some aspects of the present invention.It should be understood that the summary is not an exhaustive summary ofthe present invention. It is not intended to identify the key orcritical parts of the present invention, nor intended to limit the scopeof the present invention. It only aims to present some concepts in asimplified form as a prelude to the more detailed description that is tobe discussed later.

An object of the present invention is to provide an apparatus and amethod for determining a trigger timing of a CE-MRA scan so as toautomatically and accurately determine the trigger timing of the CE-MRAscan while take a blood flow velocity into consideration.

According to an aspect of the present invention, there is provided anapparatus for determining a trigger timing of a CE-MRA scan. Theapparatus includes: a blood flow velocity acquisition unit configured toacquire a blood flow velocity of a target vessel; and a trigger timingdetermination unit configured to determine the trigger timing forperforming the CE-MAR scan on a CE-MRA scan region according to theblood flow velocity and a predetermined image acquisition conditionduring a monitoring scan.

According to another aspect of the present invention, there is provideda method for determining a trigger timing of a CE-MRA scan. The methodincludes: acquiring a blood flow velocity of a target vessel; anddetermining the trigger timing for performing the CE-MAR scan on aCE-MRA scan region according to the blood flow velocity and apredetermined image acquisition condition during a monitoring scan.

Further, according to still another aspect of the present invention,there is provided a computer program for realizing the aforementionedmethod.

Additionally, according to still another aspect of the presentinvention, there is provided a computer program product, which is in theform of a medium at least readable to a computer, and on which computerprogram codes are recorded to realize the aforementioned method.

Embodiments of the present invention are described below with referenceto the accompanying drawings. The elements and features described in afigure or an embodiment of the present invention can be combined withthe elements and features shown in one or more other figures orembodiments. It should be noted that, for the purpose of clarity,representations and descriptions of elements and processes which areknown to those skilled in the art or are not related to the presentinvention, are not presented in the drawings and the description.

The method for determining a trigger timing of a CE-MRA scan accordingto embodiments of the present invention is described below withreference to FIG. 2 to FIG. 10.

FIG. 2 is a schematic flow chart illustrating a method for determining atrigger timing of a CE-MRA scan according to an embodiment of thepresent invention. In this method, a blood flow velocity of a targetvessel is acquired in step S210.

A predetermined blood flow velocity may be used in the method accordingto the embodiment of the present invention. For example, a predeterminedblood flow velocity that is received from outside may be used as theblood flow velocity of the target vessel. The predetermined blood flowvelocity may be, for example, a previous measurement result of anindividual to be scanned, or a statistical blood flow velocity of agroup to which the individual to be scanned belongs.

An actual blood flow velocity of the target vessel may also be used inthe method according to the embodiment of the present invention. As theblood flow velocities are different depending on the individuals to bescanned, the use of an actual blood flow velocity can allow thedetermined trigger timing more accurate.

In an embodiment of the present invention, a plurality of time-phaseimages are acquired through monitoring scans on a monitor region, andthen are used to detect a blood flow velocity of the target vessel. Theactual blood flow velocity can be detected using various appropriatemethods existing in the prior art. As an example rather than alimitation, in an embodiment of the present invention, a target vesselmay be detected in a plurality of time-phase images, and then, a bloodflow velocity of the target vessel is calculated according to adifference of the lengths of the target vessel in any two of theplurality of time-phase images and the time interval between the twotime-phase images. The blood flow velocity is equal to the difference ofthe lengths divided by the time interval. Certainly, the aforementionedmethod is only an example, and there may be other blood flow velocitycalculation methods. For example, the blood flow velocity of the targetvessel may be obtained by averaging the blood flow velocities calculatedbased on each two of the plurality of time-phase images. Such methodsfor calculating the blood flow velocity are not listed here one by one.

In a fluoroscopic image acquired by the monitoring scans, the part wherethe contrast agent locates generally has a higher brightness than thebrightness of the other parts in the image. Therefore, the contrastagent flowing in the target vessel can be easily identified in thefluoroscopic image so as to identify the target vessel. The flow speedof the contrast agent represents the flow speed of the blood in thetarget vessel. The length of the detected target vessel can berepresented by the length of the identified contrast agent.

Then, in step S220, a trigger timing for performing a CE-MAR scan on aCE-MRA scan region is determined during the monitoring scan periodaccording to the blood flow velocity and a predetermined imageacquisition condition. Specifically, a time that is needed from thetriggering of a CE-MRA scan to the acquisition of an effective CE-MRAscan image is determined according to the image acquisition condition.If an effective CE-MRA scan image is acquired at the time point at whichthe concentration of the contrast agent reaches a peak value in the ROI(scan region), the triggering of the CE-MRA scan needs to be advancedthe time (also referred to as a scan lead time) that is needed from thetriggering of a CE-MRA scan to the acquisition of an effective CE-MRAscan image. The trigger timing of the CE-MRA scan is determinedaccording to the blood flow velocity and the scan lead time.

In a CE-MRA system, the asynchrony of the time point when the CE-MPAscan is triggered and the time point when an effective CE-MRA scan imageis acquired is closely related to the image acquisition condition.First, the scan sequences used for a monitoring scan and a CE-MRA scanare different, so it takes a time period (hereinafter referred to as asequence switching time) to switch from the monitoring scan to theCE-MRA scan. In the same system, the sequence switching time is relatedto the type of the sequence used for a CE-MRA scan. Certainly, thesequence switching time may be different in different systems.Secondarily, a k-space filling method is generally used in a CE-MRA scanto form a CE-MRA image. In the k-space filling method, the CE-MRA imageformed at the time when the center of the k-space is filled has theoptimal quality. The time elapsed from the time point when a k-spacefilling is started to the time point when the center of the k-space isfilled is called a k-space centric-filling time. The k-spacecentric-filling time is related to the type of the k-space fillingmethod. For example, in a sequential k-space e filling method, thek-space centric-filling time is half of a complete k-space filling timeTA, that is, TA/2. In a center-preferential k-space filling method, thek-space centric-filling time is zero. Therefore, preferably but notnecessarily, the image acquisition condition of the type of a k-space efilling method may be taken into consideration so as to acquire ahigh-quality CE-MRA image.

In order to facilitate understanding, FIG. 3 shows a schematic diagramillustrating a time period between the time point when a CE-MRA scan istriggered and the time point when an effective CE-MRA scan image isacquired. Ideally, an effective CE-MRA scan image is acquired at thetime point when the concentration of the contrast agent reaches a peakvalue. As shown in FIG. 3, a time period t1 and a time period t2 elapsefrom the time point when the scan is triggered to the time point whenthe concentration of the contrast agent reaches the peak value. Here, t1represents a sequence switching time, and t2 represents a k-spacecentric-filling time. TA represents the time for a complete k-spacefilling. In the example shown in FIG. 3, the k-space centric-fillingtime is taken into consideration. The image scanned when the center ofthe k-space is filled has the optimal quality. However, it should beappreciated that the k-space centric-filling time may not be taken intoconsideration.

It can be seen from FIG. 3 that if the CE-MRA scan is triggeredmanually, the operator of the CE-MRA system needs to be skilled indetermining the trigger timing according to various image acquisitionconditions. In addition, as manual operations have a poor consistencyand the determined trigger timing may be different at each time, thetime between the time point when an effective CE-MRA scan image isacquired and the time point when the concentration of the contrast agentreaches the peak value may be different, resulting in a difference incontrasts of the CE-MRA scan images.

In view of this, in the method according to an embodiment of the presentinvention, a trigger timing for performing a CE-MAR scan on a CE-MRAscan region is determined according to a blood flow velocity and apredetermined image acquisition condition.

FIG. 4 is a schematic flow chart illustrating a step of determining atrigger timing according to an embodiment of the present invention. Inthis embodiment, the image acquisition condition taken intoconsideration is the type of a sequence for the CE-MRA scan. As shown inFIG. 4, in step S410, a sequence switching time is determined as a scanlead time according to the sequence type for the CE-MRA scan. Thesequence switching time is the time needed for switching from amonitoring scan to a CE-MRA scan of the sequence type. In step S420, thetrigger timing is determined according to the blood flow velocity andthe scan lead time. The details of the determining of the trigger timingaccording to the blood flow velocity and the scan lead time will bedescribed later.

FIG. 5 is a schematic flow chart illustrating a step of determining atrigger timing according to another embodiment of the present invention.In this embodiment, the following two image acquisition conditions aretaken into consideration: the type of a sequence for the CE-MRA scan,and the type of a k-space filling method to be used in the CE-MRA scan.As shown in FIG. 5, in step S510, a sequence switching time isdetermined according to the type of the sequence for the CE-MRA scan. Instep S520, a k-space centric-filling time is determined according to thetype of the k-space filling method. In step S530, the sequence switchingtime and the k-space centric-filling time are summed as a scan leadtime. Then, in step S540, the trigger timing of the CE-MRA scan isdetermined according to the blood flow velocity and the scan lead time.

It should be appreciated that in the case of the same sequence type ofCE-MRA scan, different CE-MRA systems may have different sequenceswitching times. The sequence switching time and the type of a k-spacefilling method for a CE-MRA system are generally predetermined asparameters of the CE-MRA system, and can be acquired conveniently whenit is needed to use these parameters. The k-space centric-filling time,which is corresponding to the type of the k-space filling method, can becalculated using any existing appropriate method.

After the trigger timing of the CE-MRA scan is determined, the CE-MRAscan can be triggered manually or automatically as needed. For example,the CE-MRA scan can be triggered manually by the operator thoughpressing a CE-MRA scan button, or be triggered automatically with asignal.

As examples, several embodiments of determining a trigger timingaccording to a blood flow velocity and a scan lead time are describedbelow.

1. Position Triggering

According to an embodiment of the present invention, a trigger timing ofa CE-MRA scan is determined according to the position of a contrastagent.

First, a scan lead distance is calculated according to a blood flowvelocity and a scan lead time. The scan lead distance is a product ofthe blood flow velocity and the scan lead time. As stated above, thescan lead time is the time needed from the triggering of a CE-MRA scanto the acquisition of an effective CE-MRA scan image. Accordingly, thescan lead distance represents a distance that the blood flows throughfrom the time point when the CE-MRA is triggered to the time point whenan effective scanned CE-MRA is acquired.

Then, a trigger position is determined according to the scan leaddistance and a CE-MRA scan region. Considering the scan lead distance,the trigger position is set at a position that a position for acquiringan effective CE-MRA scan image is to reach after being moved the scanlead distance in a direction reverse to the blood flow direction. Ingeneral, the position where an effective CE-MRA scan image is acquiredis substantially overlapped with a downstream boundary of the CE-MRAscan region in the blood flow direction. That is, the image acquired bythe CE-MRA scan is the image at the time point when the contrast agentarrives at the downstream boundary of the scan region. In this way, theacquired CE-MRA scan image can clearly present the whole outline of thetarget vessel in the ROI.

In order to facilitate understanding, FIG. 6 is a schematic diagramillustrating a trigger position according to an embodiment of thepresent invention. In FIG. 6, the reference sign “Offset” represents ascan lead distance, which is equal to a product of a blood flow velocityV and a scan lead time T. The solid line in the horizontal directionrepresents a position where an effective CE-MRA scan image is acquired.The dotted line in the horizontal direction represents a position wherea CE-MRA scan is triggered.

A CE-MRA scan is triggered when it is detected through a monitoring scanthat the contrast agent in the target vessel arrives at the triggerposition.

In practical applications, in order to provide a manual triggeringmechanism, the determined trigger position may be displayed on afluoroscopic image acquired from the monitoring scan. The operator cantrigger a CE-MRA scan manually when seeing that the contrast flows andarrives at the trigger position.

Additionally, in a variation of this embodiment, when the determinedtrigger position is outside the monitor region for a monitoring scan,the monitor region can be expanded automatically such that the triggerposition is in the expanded monitor region. In this way, the methodaccording to the embodiment becomes more robust. The monitor region canbe expanded using various methods that are existing in the prior art orwill be developed in future. These methods are not described in detailherein in order not to obscure the present invention.

2. Countdown Triggering

According to another embodiment of the present invention, a triggertiming of a CE-MRA scan is determined through countdown.

First, a residual trigger time is calculated according to a blood flowvelocity, a CE-MRA region and a position at which a contrast agent in atarget vessel currently arrives and which is detected through amonitoring scan. The residual trigger time is the time needed for thecontrast agent to flow from the current position until the CE-MRA scanis triggered. Ideally, the residual trigger time is equal to a distancebetween the current position of the contrast agent in the target vesseland a downstream boundary (where an effective CE-MRA scan image isgenerally acquired) of the CE-MRA region in the blood flow directiondivided by the blood flow velocity.

Considering the fact that there is a time period, i.e. a scan lead time,from the triggering to the acquisition of an effective CE-MRA scanimage, the scan lead time is subtracted from the residual trigger time.

It is determined to trigger the CE-MRA scan when it is determinedthrough countdown that the residual trigger time subtracted by the scanlead time has elapsed.

In practical applications, in order to provide a manual triggeringmechanism, the residual trigger time may be displayed on a fluoroscopicimage acquired from a monitoring scan in a countdown manner. Theoperator can trigger the CE-MRA scan manually when seeing that theresidual trigger time is zero or approximates to zero.

The method in this embodiment has no limitation on the trigger position,and will not be influenced no matter the trigger position is in oroutside the scan region.

3. Position and Countdown Combined Triggering

The time needed for a CE-MRA system to display a frame of image isreferred to as a machine time. For a monitoring scan, the machine timeis substantially equal to the inter-frame time interval of themonitoring scan. In the case of using position triggering, if thetrigger timing is during a machine time, a CE-MRA scan may be triggeredlater. For example, the contrast agent may not arrive at the triggerposition in a frame of image but exceed the trigger position in the nextframe of image. Therefore, the triggering of the CE-MRA scan in the nextframe of image is late, missing the time point at which theconcentration of the contrast agent reaches the peak value.

In view of this, according to another embodiment of the presentinvention, a trigger timing of a CE-MRA scan is determined by combiningthe trigger position and the countdown. In the embodiment, a triggertiming is determined through the following steps of:

a) calculating a scan lead distance L according to a blood flow velocityand a scan lead time;

b) determining a trigger position P according to the scan lead distanceand a CE-MRA scan region;

c) calculating, according to the blood flow velocity, a time T_(tr)needed for a contrast agent in the target vessel to flow to the triggerposition from the current position of the contrast agent detectedthrough a monitoring scan, as a residual trigger time;

d) performing a modular operation on the residual trigger time T_(tr)with an inter-frame time interval T_(intv) of the monitoring scan as amodulus: r=T_(tr) % T_(intv), and assuming the quotient resulting fromthe modular operation is m;

e) if the remainder r resulting from the modular operation is not zero,

starting to count down when m fluoroscopic images have been displayed,that is, when the number of the frames scanned through the monitoringscan is equal to the quotient m resulting from the modular operation,and

determining triggering a CE-MRA scan when it is determined through thecountdown that a time equal to the remainder r resulting from themodular operation has elapsed;

f) if the remainder r resulting from the modular operation is zero,determining triggering the CE-MRA scan when it is detected through themonitoring scan that the contrast agent in the target vessel arrives atthe trigger position.

In the steps above, steps a), b) and c) can be exchanged in executionorder without limitation.

By using the method provided in this embodiment, a trigger timing can bedetermined accurately in the case that the trigger timing is during amachine time.

4. Frame Number and Countdown Combined Triggering

As an alternative of the above embodiment in which the position and thecountdown are combined to determine a trigger timing, in anotherembodiment of the present invention, a trigger timing of a CE-MRA scanis determined by combining a frame number and the countdown.

In this embodiment, the step of determining a trigger timing includesthe following steps of:

a) calculating, according to the blood flow velocity, a time T_(tr)needed for a contrast agent in the target vessel to flow to the triggerposition from the current position of the contrast agent detectedthrough a monitoring scan as a residual trigger time;

b) performing a modular operation on the residual trigger time T_(tr)with an inter-frame time interval T_(intv) of the monitoring scan as amodulus: r=T_(tr) % T_(intv), and assuming the quotient resulting fromthe modular operation is m;

c) if the remainder r resulting from the modular operation is not zero,

starting to count down when m fluoroscopic images have been displayed,that is, when the number of the frames scanned through the monitoringscan is equal to the quotient m resulting from the modular operation,and

determining triggering a CE-MRA scan when it is determined through thecountdown that a time equal to the remainder r resulting from themodular operation has elapsed;

d) if the remainder r resulting from the modular operation is zero,determining triggering a CE-MRA scan when m fluoroscopic images aredisplayed, that is, when the number of the frames scanned through themonitoring scan is equal to the quotient m resulting from the modularoperation.

By using the method provided in this embodiment, a trigger timing can bedetermined accurately in the case that the trigger timing is during amachine time.

Compared with the steps in the above embodiment in which a triggertiming is determined by combining a position and the countdown, it isnot necessary to calculate the trigger position in this embodiment.

In a variation of the embodiment of the present invention, the CE-MARscan is started when the residual trigger time T_(tr) elapses in thecase that the T_(tr) is shorter than the inter-frame time intervalT_(intv). The residual trigger time T_(tr) is calculated and correctedframe by frame.

Under the guide of the above description, those skilled in the art canimplement the determining of the trigger timing according to a bloodflow velocity and a scan lead time in various ways, which will not belisted herein.

In addition, in the above embodiments, the trigger timing can becorrected in real time, if needed. For example, the trigger position orthe residual trigger time can be corrected in real time according to theblood flow velocity detected in real time during the monitoring scan.

One or more target vessels may be detected in the monitor region. Forexample, two great vessels may be detected when the monitor region is atthe lower limbs of a human body. For another instance, when the monitorregion is at a pelvis, the target vessel is a tree-shaped vessel with aplurality of branches, and the number of target vessels is equal to thatof the branches. The blood flow velocities of the plurality of targetvessels may be different. According to an embodiment of the presentinvention, in the case that a plurality of target vessels are detected,the smallest one of the blood flow velocities of the plurality of targetvessels is used to determine the trigger timing. This can guarantee thatthe contrast agent arrives at all the target vessels when an effectiveCE-MRA scan image is acquired.

In order to facilitate understanding, an example of a monitor regioncontaining a plurality of target vessels is given below. This example ismerely illustrative of the present invention, but is construed aslimiting the number of target vessels.

FIG. 7a -FIG. 7b are schematic diagrams showing a monitor regioncontaining two target vessels. In this example, the lengths of the twotarget vessels are respectively L1 and L2 at a time point T1 and L1′ andL2′ at a time point T2. Then, the blood flow velocity of the left targetvessel is calculated as

${{V\; 1} = \frac{{L\; 1^{\prime}} - {L\; 1}}{{T\; 2} - {T\; 1}}},$

and the blood flow velocity of the right target vessel is calculated as

${V\; 2} = {\frac{{L\; 2^{\prime}} - {L\; 2}}{{T\; 2} - {T\; 1}}.}$

The smallest one of the V1 and the V2 (min(V1,V2)) is used as a bloodflow velocity for determining the trigger timing.

FIG. 8a -FIG. 8b are schematic diagrams showing a monitor regioncontaining tree-shaped target vessels. In this example, a target vesselhas two branches, the lengths of which are L1 and L2 respectively, at atime point T1, and has four branches, the lengths of which are P1, P2,P3 and P4 respectively, at a time point T2. That is, there are fourtarget vessels in the monitor region. Accordingly, the blood flowvelocities of the four branches are respectively calculated according tothe following formulas:

${{V\; 1} = \frac{{P\; 1} - {L\; 1}}{{T\; 2} - {T\; 1}}},{{V\; 2} = \frac{{P\; 2} - {L\; 1}}{{T\; 2} - {T\; 1}}},{{V\; 3} = {{\frac{{P\; 3} - {L\; 2}}{{T\; 2} - {T\; 1}}\mspace{14mu} {and}\mspace{14mu} V\; 4} = {\frac{{P\; 4} - {L\; 2}}{{T\; 2} - {T\; 1}}.}}}$

The smallest one of the four velocities (min(V1,V2,V3,V4)) is used as ablood flow velocity for determining the trigger timing.

In the method for determining a trigger timing of a CE-MRA scanaccording to embodiments of the present invention, the monitor regioncan be manually set as in the prior art. In order to set the monitorregion more accurately, according to an embodiment of the presentinvention, the monitor region for a monitoring scan may be determinedaccording to the predetermined blood flow velocity of the target vessel,the predetermined image acquisition condition and the CE-MRA scan regionbefore starting the monitoring scan.

In the prior art, in order to facilitate the operation of the operator,a monitor region is generally set in such a way that a CE-MPA scan istriggered when the contrast agent flows to a downstream boundary of themonitor region in the blood flow direction. Therefore, in the embodimentof the present invention, the downstream boundary of the monitor regionmay also be set to substantially correspond to the trigger position,while there is no limitation to the upstream boundary of the monitorregion in the blood flow direction. Certainly, the present invention isnot limited to this case, and the downstream boundary of the monitorregion can also be located downstream from the trigger position. Inaddition, in the case that the CE-MRA scan is triggered throughcountdown rather than though determining the position of the contrastagent, as described in some above-described embodiments, the downstreamboundary of the monitor region may also be located upstream from anactual trigger position.

As a specific example, FIG. 9 shows a schematic flow chart illustratinga step of determining a monitor region according to an embodiment of thepresent invention. In this embodiment, the image acquisition conditionincludes the type of a sequence for the CE-MRA scan. As shown in FIG. 9,in step S910, a sequence switching time is determined according to thetype of the sequence for the CE-MRA scan as a scan lead time. In stepS920, a scan lead distance is calculated according to a blood flowvelocity and the scan lead time. In step S930, a downstream boundary ofthe monitor region in a blood flow direction of the target vessel isdetermined according to the scan lead distance and a CE-MRA scan region.Specifically, the downstream boundary of the monitor region is set at aposition that the downstream boundary of the CE-MRA scan region in theblood flow direction is to reach after being moved the scan leaddistance in a direction inverse to the blood flow direction.

FIG. 10 is a schematic flow chart illustrating a step of determining amonitor region according to another embodiment of the present invention.In this embodiment, the image acquisition condition includes the type ofthe sequence for the CE-MRA scan and the type of the k-space fillingmethod to be used in the CE-MRA scan. As shown in FIG. 10, in stepS1010, a sequence switching time is determined according to the type ofthe sequence for the CE-MRA scan as a scan lead time. In step S1020, ak-space centric-filling time is determined according to the type of thek-space filling method. In step S1030, the sequence switching time andthe k-space centric-filling time are summed as a scan lead time. In stepS1040, a scan lead distance is calculated according to a blood flowvelocity and the scan lead time. In step S1050, a downstream boundary ofthe monitor region in a blood flow direction of the target vessel isdetermined according to the scan lead distance and the CE-MRA scanregion. Specifically, similar to the embodiment shown in FIG. 9, thedownstream boundary of the monitor region is set at a position that thedownstream boundary of the CE-MRA scan region in the blood flowdirection is to reach after being moved the scan lead distance in adirection inverse to the blood flow direction.

In the embodiments shown in FIG. 9 and FIG. 10, the monitor region andthe CE-MRA scan region are set in the same plane as in the prior art.

An apparatus for determining a trigger timing of a CE-MRA scan accordingto embodiments of the present invention is described below withreference to FIG. 11-FIG. 21.

FIG. 11 is a schematic block diagram illustrating an apparatus fordetermining a trigger timing of a CE-MRA scan according to an embodimentof the present invention. As shown in FIG. 11, an apparatus 1100 fordetermining a trigger timing of a CE-MRA scan includes a blood flowvelocity acquisition unit 1110 and a trigger timing determination unit1120. The blood flow velocity acquisition unit 1110 is configured toacquire a blood flow velocity of a target vessel.

A predetermined blood flow velocity may be used in the apparatusaccording to an embodiment of the present invention. According to anembodiment of the present invention, the blood flow velocity acquisitionunit 1110 is further configured to receive from outside a predeterminedblood flow velocity as the blood flow velocity of the target vessel.

An actual blood flow velocity of the target vessel may also be used inthe apparatus according to an embodiment of the present invention. FIG.12 is a schematic block diagram illustrating a blood flow velocityacquisition unit according to an embodiment of the present invention. Inthis embodiment, the blood flow velocity acquisition unit 1110 mayinclude an image acquisition unit 1210 and a blood flow velocitydetection unit 1220. The image acquisition unit 1210 is configured toacquire a plurality of time-phase images obtained by a monitoring scanon a monitor region. The blood flow velocity detection unit 1220 isconfigured to detect the blood flow velocity of the target vessel usingthe plurality of time-phase images.

The blood flow velocity detection unit 1220 may detect an actual bloodflow velocity using various appropriate methods available in the priorart. As an example rather than a limitation, according to an embodimentof the present invention, the blood flow velocity detection unit 1220includes a vessel detection unit and a blood flow velocity calculator(not shown). The vessel detection unit is configured to detect a targetvessel in the plurality of time-phase images. The blood flow velocitycalculator is configured to calculate the blood flow velocity of thetarget vessel according to a difference of the lengths of the targetvessel in any two of the plurality of time-phase images and a timeinterval between the two time-phase images. The blood flow velocity isequal to the difference of the lengths divided by the time interval.Certainly, the aforementioned method is only an example, and there maybe other blood flow velocity calculation methods. For example, the bloodflow velocity of the target vessel may be obtained by averaging theblood flow velocities calculated based on each two of the plurality oftime-phase images.

Further, according to another embodiment of the present invention, inthe case that a plurality of target vessels are detected by the bloodflow velocity detection unit 1220, the blood flow velocity detectionunit uses the smallest one of the blood flow velocities of the pluralityof target vessels calculated by the blood flow velocity calculator as ablood flow velocity for determining the trigger timing. This canguarantee that the contrast agent arrives at all the target vessels whenan effective CE-MRA scan image is acquired.

In FIG. 11, the trigger timing determination unit 1120 is configured todetermine the trigger timing for performing the CE-MAR scan on a CE-MRAscan region according to the blood flow velocity and a predeterminedimage acquisition condition during a monitoring scan. Specifically, thetrigger timing determination unit 1120 may determine, according to theimage acquisition condition, a time needed from the triggering of theCE-MRA scan to the acquisition of an effective CE-MRA scan image, i.e. ascan lead time. Then the trigger timing determination unit 1120determines the trigger timing of the CE-MRA scan according to the bloodflow velocity and the scan lead time.

FIG. 13 is a schematic block diagram illustrating a trigger timingdetermination unit according to an embodiment of the present invention.In the embodiment shown in FIG. 13, the image acquisition conditionincludes the type of a sequence for the CE-MRA scan. As shown in FIG.13, the trigger timing determination unit 1120 includes a scan lead timedetermination unit 1310 and a trigger timing determination subunit 1320.The scan lead time determination unit 1310 is configured to determine asequence switching time according to the type of the sequence used forthe CE-MRA scan as a scan lead time. The trigger timing determinationsubunit 1320 is configured to determine the trigger timing according tothe blood flow velocity and the scan lead time.

FIG. 14 is a schematic block diagram illustrating a trigger timingdetermination unit according to another embodiment of the presentinvention. In FIG. 14, the image acquisition condition includes the typeof a sequence for the CE-MRA scan and the type of a k-space fillingmethod to be used in the CE-MRA scan. The trigger timing determinationunit 1120 includes a scan lead time determination unit 1310 and atrigger timing determination subunit 1320. The scan lead timedetermination unit 1310 is configured to determine a scan lead time, adincludes a sequence switching time determination unit 1311, a k-spacecentric-filling time determination unit 1312 and a summation unit 1313.The sequence switching time determination unit 1311 is configured todetermine a sequence switching time according to the type of a sequenceto be used in the CE-MRA scan. The k-space centric-filling timedetermination unit 1312 is configured to determine a k-spacecentric-filling time according to the type of a k-space filling method.The summation unit 1313 is configured to sum the sequence switching timeand the k-space centric-filling time as the scan lead time. The triggertiming determination subunit 1320 is configured to determine the triggertiming according to the blood flow velocity and the scan lead time. Inthis embodiment, the k-space centric-filling time is included in thescan lead time so that a CE-MRA image of a better quality can beacquired.

After the trigger timing of the scan is determined, the CE-MRA scan canbe triggered manually, or be triggered automatically by the triggertiming determination unit 1120, depending on the requirement. Forexample, the CE-MRA scan can be triggered by the operator throughpressing a CE-MRA scan button, or be triggered automatically by thetrigger timing determination unit 1120 via a signal.

Several specific embodiments of the trigger timing determination subunitare described below as examples.

FIG. 15 is a schematic block diagram illustrating a trigger timingdetermination subunit according to an embodiment of the presentinvention. In this embodiment, a trigger timing determination subunit1500 determines the trigger timing based on a position. As shown in FIG.15, the trigger timing determination subunit 1500 includes a triggerposition determination unit 1510 and a trigger position monitor 1520.The trigger position determination unit 1510 is configured to calculatea scan lead distance according to the blood flow velocity and the scanlead time, and determine a trigger position according to the scan leaddistance and the CE-MRA scan region. The scan lead distance is a productof the blood flow velocity and the scan lead time. The trigger positionmay be set at a position that a position for acquiring an effectiveCE-MRA scan image is to reach after being moved the scan lead distancein a direction reverse to the blood flow direction. The trigger positionmonitor 1520 is configured to determining triggering the CE-MRA scanwhen it is detected by the monitoring scan that the contrast agent inthe target vessel arrives at the trigger position.

In a variation of this embodiment, the apparatus for determining atrigger timing of a CE-MRA scan may further include a monitor regionadjustment unit (not shown). The monitor region adjustment unit isconfigured to expand a monitor region for a monitoring scanautomatically when the trigger position determined by the triggingposition determination unit 1510 is outside the monitor region, suchthat the trigger position is in the expanded monitor region.

FIG. 16 is a schematic block diagram illustrating a trigger timingdetermination subunit according to another embodiment of the presentinvention. In this embodiment, a trigger timing determination subunit1600 determines the trigger timing through countdown. As shown in FIG.16, the trigger timing determination subunit 1600 includes a residualtrigger time calculator 1610 and a residual trigger time monitor 1620.The residual trigger time calculator 1610 is configured to calculate aresidual trigger time according to the blood flow velocity, the CE-MRAscan region and a position at which a contrast agent in the targetvessel currently arrives and which is detected through a monitoringscan, and subtract the scan lead time from the residual trigger time.The residual trigger time monitor 1620 is configured to determinetriggering the CE-MAR scan when it is determined through countdown thatthe residual trigger time has elapsed. In this embodiment, whether ornot the trigger position is in the monitor region does not influence thetrigger timing determination subunit.

FIG. 17 is a schematic block diagram illustrating a trigger timingdetermination subunit according to another embodiment of the presentinvention. In this embodiment, a trigger timing determination subunit1700 determines the trigger timing based on a position and countdown. Asshown in FIG. 17, the trigger timing determination subunit 1700 includesa trigger position determination unit 1710, a residual trigger timecalculator 1720, a modular operation unit 1730, a residual trigger timemonitor 1740 and a trigger position monitor 1750. The trigger positiondetermination unit 1710 is configured to calculate a scan lead distanceaccording to the blood flow velocity and the scan lead time, anddetermine a trigger position according to the scan lead distance and aCE-MRA scan region. The residual trigger time calculator 1720 isconfigured to calculate, according to the blood flow velocity, a timeneeded for the contrast agent in the target vessel to flow to thetrigger position from a current position of the contrast agent detectedthrough the monitoring scan, as the residual trigger time. The modularoperation unit 1730 is configured to perform a modular operation on theresidual trigger time with an inter-frame time interval of themonitoring scan as a modulus. The modular operation unit 1730 activatesthe residual time monitor 1740 if the remainder resulting from themodular operation is not zero. The modular operation unit 1730 activatesthe trigger position monitor 1750 if the remainder resulting from themodular operation is zero. The residual trigger time monitor 1740 isconfigured to start to count down when the same number of frames as aquotient resulting from the modular operation have been scanned throughthe monitoring scan. When it is determined through the countdown that atime equal to a remainder resulting from the modular operation haselapsed, the residual trigger time monitor 1740 determines triggeringthe CE-MRA scan. The trigger position monitor 1750 is configured todetermine triggering the CE-MRA scan when it is detected through themonitoring scan that the contrast agent in the target vessel arrives atthe trigger position. Through the trigger timing determination subunitaccording to this embodiment, the trigger timing can be determinedaccurately in the case that the trigger timing is during a machine time.

FIG. 18 is a schematic block diagram illustrating a trigger timingdetermination subunit according to another embodiment of the presentinvention. In this embodiment, a trigger timing determination subunit1800 determines the trigger timing based on a combination of a framenumber and countdown. As shown in FIG. 18, the trigger timingdetermination subunit 1800 includes a residual trigger time calculator1810, a modular operation unit 1820, a residual time monitor 1830 and aframe number monitor 1840. The residual trigger time calculator 1810 isconfigured to calculate, according to the blood flow velocity, a timeneeded for the contrast agent in the target vessel to flow to thetrigger position from a current position of the contrast agent detectedthrough a monitoring scan, as the residual trigger time. The modularoperation unit 1820 is configured to perform a modular operation on theresidual trigger time with an inter-frame time interval of themonitoring scan as a modulus. The modular operation unit 1820 activatesthe residual time monitor 1830 if a remainder resulting from the modularoperation is not zero. The modular operation unit 1820 activates theframe number monitor 1840 if a remainder resulting from the modularoperation is zero. The residual trigger time monitor 1830 is configuredto start to count down when the same number of frames as a quotientresulting from the modular operation have been scanned through themonitoring scan. The residual trigger time monitor 1830 triggers theCE-MRA scan when it is determined though the countdown that a time equalto the remainder resulting from the modular operation has elapsed. Theframe number monitor 1840 is configured to trigger the CE-MRA scan whenthe same number of frames as a quotient resulting from the modularoperation have been scanned through the monitoring scan. Through thetrigger timing determination subunit provided in this embodiment, atrigger timing can be determined accurately in the case that the triggertiming is during a machine time. Compared with the trigger timingdetermination subunit shown in FIG. 18, the trigger timing determinationsubunit provided in this embodiment needs not to calculate a triggerposition.

Under the guide of the above description, those skilled in the art canimplement the trigger timing determination subunit in various ways,which will not be listed herein.

In addition, in the above embodiments, the trigger timing determinationunit 1120 may further configured to correct the trigger timing in realtime as required. For example, the trigger position or the residualtrigger time can be corrected in real time according to the blood flowvelocity detected in real time during the monitoring scan.

The apparatus for determining a trigger timing of a CE-MRA scanaccording to an embodiment may further include a monitor regiondetermination unit. The monitor region determination unit is configuredto determine a monitor region for a monitoring scan automatically beforethe monitoring scan is started.

FIG. 19 is a schematic block diagram illustrating an apparatus fordetermining a trigger timing of a CE-MRA scan according to anotherembodiment of the present invention. Compared with the apparatus shownin FIG. 11, the apparatus 1900 shown in FIG. 19 is additionally providedwith a monitor region determination unit 1930. The monitor regiondetermination unit 1930 is configured to determine, before themonitoring scan is started, a monitor region for the monitoring scanaccording to the predetermined blood flow velocity of the target vessel,the predetermined image acquisition condition and a CE-MRA scan region.The blood flow velocity acquisition unit 1910 has substantially the samefunction with the blood flow velocity acquisition unit 1110 of theapparatus 1100 shown in FIG. 11. The trigger timing determination unit1920 has substantially the same function with the trigger timingdetermination unit 1120 of the apparatus 1110 shown in FIG. 11. Themonitor region determination unit 1930 can receive a predetermined bloodflow velocity from outside, or acquire a predetermined blood flowvelocity using the blood flow velocity acquisition unit 1910.

The downstream boundary of the monitor region in the blood flowdirection can be set at substantially the same position as the triggerposition. Therefore, the monitor region determination unit 1930 candetermine the downstream boundary of the monitor region using the methodused by the trigger position determination unit. There is no limitationto the upstream boundary of the monitor region in the blood flowdirection. Further, as stated above, the downstream boundary of themonitor region may also be located at a position different from thetrigger position.

FIG. 20 is a schematic block diagram illustrating a monitor regiondetermination unit according to an embodiment of the present invention.In this embodiment, the image acquisition condition includes the type ofa sequence for the CE-MRA scan. As shown in FIG. 20, the monitor regiondetermination unit 1930 includes a scan lead time determination unit2010, a scan lead distance determination unit 2020 and a boundarydetermination unit 2030. The scan lead time determination unit 2010 isconfigured to determine a sequence switching time according to the typeof a sequence for the CE-MRA scan, as a scan lead time. The scan leaddistance determination unit 2020 is configured to calculate a scan leaddistance according to the blood flow velocity and the scan lead time.The boundary determination unit 2030 is configured to determine adownstream boundary of the monitor region in a blood flow direction ofthe target vessel according to the scan lead distance and the CE-MRAscan region. Specifically, the downstream boundary of the monitor regionis set at a position that the downstream boundary of the CE-MRA scanregion in the blood flow direction is to reach after being moved thescan lead distance in a direction inverse to the blood flow direction.

FIG. 21 is a schematic block diagram illustrating a monitor regiondetermination unit according to another embodiment of the presentinvention. In this embodiment, the image acquisition condition includesthe type of a sequence for the CE-MRA scan and the type of a k-spacefilling method to be used in the CE-MRA scan. As shown in FIG. 21, themonitor region determination unit 1930 includes a scan lead timedetermination unit 2110, a scan lead distance determination unit 2120and a boundary determination unit 2130. The scan lead time determinationunit 2110 is configured to determine a scan lead time, and includes asequence switching time determination unit 2111, a k-spacecentric-filling time determination unit 2112 and a summation unit 2113.The sequence switching time determination unit 2111 is configured todetermine a sequence switching time according to the type of a sequencefor the CE-MRA scan. The k-space centric-filling time determination unit2112 is configured to determine a k-space centric-filling time accordingto the type of a k-space filling method. The summation unit 2113 isconfigured to sum the sequence switching time and the k-spacecentric-filling time as a scan lead time. The scan lead distancedetermination unit 2120 is configured to calculate a scan lead distanceaccording to the blood flow velocity and the scan lead time. Theboundary determination unit 2130 is configured to determine a downstreamboundary of the monitor region in the blood flow direction of the targetvessel according to the scan lead distance and the CE-MRA scan region.Similarly, the downstream boundary of the monitor region is set at aposition that the downstream boundary of the CE-MRA scan region in theblood flow direction is to reach after being moved the scan leaddistance in a direction inverse to the blood flow direction.

In addition, the monitor region determination unit may be furtherconfigured to set the monitor region in the plane where a CE-MRA scanregion is located. This is the same as in the prior art and needs not bedescribed here in detail.

More detailed operations of each unit in the apparatus according to theembodiments of the present invention can be understood with reference torelated description on the method according to the embodiments of thepresent invention and is therefore not repeated here.

The method and apparatus for determining a trigger timing of a CE-MRAscan according to the embodiments of the present invention determine thetrigger timing by taking a blood flow velocity into consideration, andcan determine the trigger timing of the CE-MRA scan automatically andaccurately.

As an example, the respective steps of the method for determining atrigger timing of a CE-MRA scan and the respective modules and/or unitsof the apparatus according to the embodiments of the present inventionmay be implemented as software, firmware, hardware or a combinationthereof in a CE-MRA system, and serve as a part of the CE-MRA system. Asanother example, the respective steps of the above-described method andthe respective modules and/or units of the above-described apparatus maybe implemented as an apparatus separately from a CE-MRA system. Thespecific means or approaches that may be used in configuring the modulesand units in the above-described apparatus through software, firmware,hardware or any combination thereof are well known to those skilled inthe art and therefore will not be repeatedly described.

As an example, the steps of the above-described method and the modulesand/or units of the above-described apparatus may be implemented assoftware, firmware, hardware or a combination thereof. In the case wherethe steps of the above-described method and the modules and/or units ofthe above-described apparatus are implemented through software orfirmware, a program constituting the software for implementing theabove-described method may be installed in a computer (e.g. the generalcomputer 2200 shown in FIG. 22) with a dedicate hardware structure froma storage medium or a network, and the computer, when installed withvarious programs, is capable of perform various functions.

In FIG. 22, a central processing unit (i.e. CPU) 2201 executes variousprocesses according to the programs stored in a read-only memory (ROM)2202 or programs loaded to a random access memory (RAM) 2203 from astorage part 2208. Data needed by the CPU 2201 in executing the variousprocesses are also stored in the RAM 2203 as required. The CPU 2201, theROM 2202 and the RAM 2203 are connected with each other via a bus 2204.An input/output interface 2205 is also connected to the bus 2204.

The following parts are connected to the input/output (I/O) interface2205: an input part 2206 (including a keyboard, a mouse and etc.), anoutput part 2207 (including a display such as a cathode-ray tube (CRT)or a liquid crystal display (LCD), and a speaker, etc.), the storagepart 2208 (including a hard disk, etc.), and a communication part 2209(including a network interface card such as an LAN card, a MODEM andetc.). The communication part 2209 executes communication processing viaa network such as the Internet. A driver 2210 can also be connected tothe input/output interface 2205 as required. A removable medium 2211such as a magnetic disk, an optical disk, a magneto-optical disk or asemiconductor memory can be mounted on the driver 2210 as required, suchthat the computer program read out therefrom is installed into thestorage part 2208 as required.

In the case that the above series of processes are implemented bysoftware, a program constituting the software is installed from anetwork such as the Internet or from a storage medium such as theremovable medium 2211.

It is to be understood by those skilled in the art that such storagemedium is not limited to the removable medium 2211 storing programstherein and distributing the programs to a user(s) dependently from adevice. Examples of the removable medium 2211 include a magnetic disk(including a Floppy Disk (registered trademark)), an optical disk(including a Compact Disk-Read Only Memory (CD-ROM) and a DigitalVersatile Disc (DVD)), a magneto-optical disk (including a Microdisk(MD) (registered trademark)) and a semiconductor memory. Alternatively,the storage medium can be the ROM 2202, a hard disk contained in thestorage part 2208, etc., in which programs are stored and which isdistributed to a user(s) along with a device the storage medium iscontained in.

The present invention further provides a program product in whichcomputer-readable instruction codes are stored. The instruction codes,when read and executed by a machine, can execute the methods accordingto the embodiments of the present invention.

Correspondingly, the storage medium for carrying the program productstoring machine-readable instruction codes is also incorporated in thedisclosure of the present invention. The storage medium includes, but isnot limited to, a flexible disk, an optical disk, a magneto-opticaldisk, a storage card and a storage stick.

In the exemplary embodiments above, the examples are explained in whichthe apparatus 1100 performs the various types of processes describedabove; however, the exemplary embodiments are not limited to theseexamples. For example, another arrangement is acceptable in which acomputer comprising in an MRI apparatus performs the various types ofprocesses described above.

FIG. 23 is a functional block diagram depicting a configuration of anMRI apparatus 100. As shown in FIG. 23, the MRI apparatus 100 includes amagnetostatic field magnet 101, a magnetostatic field power source 102,a gradient coil 103, a gradient power source 104, a couch 105, a couchcontrolling unit 106, a transmission coil 107, a transmitting unit 108,a reception coil 109, a receiving unit 110, a sequence controlling unit120, and a computer 130. A subject P (e.g., a human body) is notincluded in the MRI apparatus 100. The configuration shown in FIG. 23 ismerely an example. For instance, the functional units included in thesequence controlling unit 120 and the computer 130 may be configured asbeing integrated together or separated, as necessary.

The magnetostatic field magnet 101 is a magnet formed in the shape of ahollow circular cylinder and generates a magnetostatic field in thespace on the inside thereof. The magnetostatic field magnet 101 may beconfigured by using, for example, a superconductive magnet. Themagnetostatic field magnet 101 is configured to be excited by receivinga supply of electric current from the magnetostatic field power source102. The magnetostatic field power source 102 supplies the electriccurrent to the magnetostatic field magnet 101. Alternatively, themagnetostatic field magnet 101 may be configured by using a permanentmagnet. In that situation, the MRI apparatus 100 does not necessarilyhave to include the magnetostatic field power source 102. It is alsoacceptable to provide the magnetostatic field power source 102separately from the MRI apparatus 100.

The gradient coil 103 is a coil formed in the shape of a hollow circularcylinder and is disposed on the inside of the magnetostatic field magnet101. The gradient coil 103 is formed by combining three coilscorresponding to X-, Y-, and Z-axes that are orthogonal to one another.These three coils individually receive a supply of electric current fromthe gradient power source 104 and generate gradient magnetic fields ofwhich the magnetic field intensities change along the X-, Y-, andZ-axes. The gradient magnetic fields on the X-, Y-, and Z-axes that aregenerated by the gradient coil 103 are, for example, a slice encodinggradient magnetic field G_(SE) (or a slice selecting gradient magneticfield G_(SS)), a phase encoding gradient magnetic field G_(PE), and afrequency encoding gradient magnetic field G_(RO), respectively. Thegradient power source 104 supplies electric current to the gradient coil103.

The couch 105 includes a couchtop 105 a on which the subject P isplaced. Under control of the couch controlling unit 106, while thesubject P is placed thereon, the couchtop 105 a is inserted into thehollow (i.e., an image taking opening) of the gradient coil 103.Normally, the couch 105 is provided so that the longitudinal directionthereof extends parallel to the central axis of the magnetostatic fieldmagnet 101. Under control of the computer 130, the couch controllingunit 106 drives the couch 105 so that the couchtop 105 a moves in thelongitudinal direction and in an up-and-down direction.

The transmission coil 107 is disposed on the inside of the gradient coil103 and generates a radio-frequency magnetic field by receiving a supplyof a Radio Frequency (RF) pulse from the transmitting unit 108. Thetransmitting unit 108 supplies the RF pulse corresponding to a Larmorfrequency, which is determined by the type of a target atom and theintensity of the magnetic field, to the transmission coil 107.

The reception coil 109 is disposed on the inside of the gradient coil103 and receives Magnetic Resonance (MR) signals emitted from thesubject P due to an influence of the radio-frequency magnetic field.When having received the MR signals, the reception coil 109 outputs thereceived MR signals to the receiving unit 110.

The transmission coil 107 and the reception coil 109 described above aremerely examples. It is acceptable to use one or more in combinationselected from among a coil having only a transmitting function, a coilhaving only a receiving function, and a coil having a transmitting andreceiving function.

The receiving unit 110 detects the MR signals being output from thereception coil 109 and generates MR data based on the detected MRsignals. More specifically, the receiving unit 110 generates the MR databy applying a digital conversion to the MR signals being output from thereception coil 109. Further, the receiving unit 110 transmits thegenerated MR data to the sequence controlling unit 120. The receivingunit 110 may be provided on a gantry device side where the magnetostaticfield magnet 101, the gradient coil 103, and like are provided.

The sequence controlling unit 120 performs an image taking process onthe subject P, by driving the gradient power source 104, thetransmitting unit 108, and the receiving unit 110, based on sequenceinformation transmitted from the computer 130. In this situation, thesequence information is information that defines a procedure forperforming the image taking process. The sequence information defines,for example, the intensity of the electric current to be supplied by thegradient power source 104 to the gradient coil 103 and the timing withwhich the electric current is to be supplied; the strength of the RFpulse to be supplied by the transmitting unit 108 to the transmissioncoil 107 and the timing with which the RF pulse is to be applied; andthe timing with which the MR signals are to be detected by the receivingunit 110. The sequence controlling unit 120 is configured by using, forexample, an integrated circuit such as an Application SpecificIntegrated Circuit (ASIC) or a Field Programmable Gate Array (FPGA), oran electronic circuit such as a Central Processing Unit (CPU) or a MicroProcessing Unit (MPU).

When the sequence controlling unit 120 has received the MR data from thereceiving unit 110, as a result of driving the gradient power source104, the transmitting unit 108, and the receiving unit 110 and takingthe image of the subject P, the sequence controlling unit 120 transfersthe received MR data to the computer 130.

The computer 130 exercises overall control of the MRI apparatus 100 andgenerates an MR image, for example. The computer 130 includes aninterface unit 131, a storage unit 132, the controlling unit 133, aninput unit 134, a display unit 135, and an image generating unit 136.

The interface unit 131 transmits the sequence information to thesequence controlling unit 120 and receives the MR data from the sequencecontrolling unit 120. When having received the MR data, the interfaceunit 131 stores the received MR data into the storage unit 132. The MRdata stored in the storage unit 132 is arranged into a k-space by thecontrolling unit 133. As a result, the storage unit 132 stores thereink-space data corresponding to a plurality of channels.

The storage unit 132 stores therein, for example, the MR data receivedby the interface unit 131, the k-space data arranged in the k-space bythe controlling unit 133, and image data generated by the imagegenerating unit 136. For example, the storage unit 132 is configured byusing a semiconductor memory element such as a Random Access Memory(RAM) or a flash memory, a hard disk, an optical disk, or the like.

The input unit 134 receives various types of instructions and inputs ofinformation from an operator. The input unit 134 is configured by usinga pointing device such as a mouse or a trackball, a selecting devicesuch as a mode changing switch, and/or an input device such as akeyboard. Under control of the controlling unit 133, the display unit135 displays various types of information such as spectrum data and theimage data. The display unit 135 is configured by using, for example, adisplay device such as a liquid crystal display device.

The controlling unit 133 exercises overall control of the MRI apparatus100. More specifically, the controlling unit 133 controls the imagetaking process by generating the sequence information based on an imagetaking condition input from the operator via the input unit 134 andtransmitting the generated sequence information to the sequencecontrolling unit 120. Further, the controlling unit 133 controls theimage generating process performed based on the MR data and controls thedisplay process realized by the display unit 135. Further, thecontrolling unit 133 reads the MR data generated by the receiving unit110 from the storage unit 132 and arranges the read MR data into thek-space. For example, the controlling unit 133 is configured by using anintegrated circuit such as an ASIC or an FPGA, or an electronic circuitsuch as a CPU or an MPU.

The image generating unit 136 reads the k-space data arranged in thek-space by the controlling unit 133 from the storage unit 132 andgenerates the MR image by applying a reconstructing process such as aFourier transform to the read k-space data.

In the above description of the specific embodiments of the presentinvention, features described and/or illustrated with respect to oneembodiment can be used in one or more other embodiments in an identicalor similar manner, be combined with features in other embodiments, orreplace features in other embodiments.

It should be emphasized that, the term “comprise/include”, as used inthe present description, refers to the presence of features, sections,steps or components, but does not exclude the presence or addition ofone or more other features, sections, steps or components.

In the above embodiments and examples, the steps and/or units arerepresented with a reference sign consisting of numbers. It should beunderstood by those of ordinary skill of the art that the referencesigns are merely intended to facilitate description and drawingdepiction, but are not to be construed as indicating the orders of thesteps and/or units nor a limitation on any other aspect.

Furthermore, the methods of the present invention are not limited tobeing executed in the temporal orders as described in the specification,but can also be executed in other temporal order, in parallel orseparately. Therefore, the execution orders of the methods described inthe present specification do not constitute a limitation to thetechnical scope of the present invention.

Although the present invention has been disclosed with reference todescriptions for the specific embodiments of the present invention, itshould be understood that all of the above mentioned embodiments andexamples are illustrative instead of limiting. Those skilled in the artcan devise various modifications, improvements or equivalents for thepresent invention, within the spirit and scope of the appended claims.The modifications, improvements or equivalents should also be consideredas being included in the protection scope of the present invention.

1. A magnetic resonance imaging apparatus for determining a triggertiming of a Contrast Enhanced Magnetic Resonance Angiography (CE-MRA)scan, comprising: a blood flow velocity acquisition unit configured toacquire a blood flow velocity of a target vessel; and a trigger timingdetermination unit configured to determine the trigger timing forperforming the CE-MAR scan on a CE-MRA scan region according to theblood flow velocity and a predetermined image acquisition conditionduring a monitoring scan.
 2. The apparatus according to claim 1, whereinthe blood flow velocity acquisition unit is further configured toreceive the blood flow velocity of the target vessel from outside. 3.The apparatus according to claim 1, wherein the blood flow velocityacquisition unit comprises: an image acquisition unit configured toacquire a plurality of time-phase images obtained by the monitoring scanon a monitor region; and a blood flow velocity detection unit configuredto detect the blood flow velocity of the target vessel using theplurality of time-phase images.
 4. The apparatus according to claim 1,wherein the image acquisition condition includes the type of a sequencefor the CE-MRA scan, and the trigger timing determination unitcomprises: a scan lead time determination unit configured to determine asequence switching time according to the type of the sequence for theCE-MRA scan as a scan lead time, wherein the sequence switching time isa time needed for switching from the monitoring scan to the CE-MRA scanof the type of the sequence; and a trigger timing determination subunitconfigured to determine the trigger timing according to the blood flowvelocity and the scan lead time.
 5. The apparatus according to claim 4,wherein the trigger timing determination subunit comprises: a triggerposition determination unit configured to calculate a scan lead distanceaccording to the blood flow velocity and the scan lead time, anddetermine a trigger position according to the scan lead distance and theCE-MRA scan region; and a trigger position monitor configured todetermine triggering the CE-MRA scan when it is detected through themonitoring scan that a contrast agent in the target vessel arrives atthe trigger position.
 6. The apparatus according to claim 5, furthercomprising: a monitor region adjustment unit configured to expand amonitor region for the monitoring scan automatically when the triggerposition is outside the monitor region, such that the trigger positionis in the expanded monitor region.
 7. The apparatus according to claim4, wherein the trigger timing determination subunit comprises: a triggerposition determination unit configured to calculate a scan lead distanceaccording to the blood flow velocity and the scan lead time, anddetermine a trigger position according to the scan lead distance and theCE-MRA scan region; a residual trigger time calculator configured tocalculate, according to the blood flow velocity, a time needed for acontrast agent in the target vessel to flow to the trigger position froma current position of the contrast agent in the target vessel detectedthrough the monitoring scan, as a residual trigger time; a modularoperation unit configured to perform a modular calculation on theresidual trigger time with an inter-frame time interval of themonitoring scan as a modulus, activate a residual trigger time monitorwhen a remainder resulting from the modular calculation is not zero, andactivate a trigger position monitor when the remainder resulting fromthe modular calculation is zero; the residual trigger time monitorconfigured to start countdown when the same number of frames as aquotient resulting from the modular operation have been scanned throughthe monitoring scan, and determine triggering the CE-MRA scan when it isdetermined through the countdown that a time equal to the remainderresulting from the modular operation has elapsed; and the triggerposition monitor configured to determine triggering the CE-MRA scan whenit is detected through the monitoring scan that the contrast agent inthe target vessel arrives at the trigger position.
 8. The apparatusaccording to claim 3, wherein the blood flow velocity detection unitcomprises: a vessel detection unit configured to detect the targetvessel in the plurality of time-phase images; and a blood flow velocitycalculator configured to calculate the blood flow velocity of the targetvessel according to a difference of the lengths of the target vessel inany two of the plurality of time-phase images and a time period betweenthe two images.
 9. The apparatus according to claim 8, wherein the bloodflow velocity detection unit is further configured to, in the case thata plurality of target vessels are detected by the vessel detection unit,determine the trigger timing using the smallest one of the blood flowvelocities of the plurality of target vessels calculated by the bloodflow velocity calculator, as the blood flow velocity for determining thetrigger timing.
 10. The apparatus according to claim 1, furthercomprising: a monitor region determination unit configured to determine,before the monitoring scan is started, a monitor region for themonitoring scan according to a predetermined blood flow velocity of thetarget vessel, the predetermined image acquisition condition and theCE-MRA scan region.
 11. The apparatus according to claim 1, wherein thetrigger timing determination unit is further configured to trigger theCE-MRA scan automatically after the trigger timing is determined. 12.The apparatus according to claim 7, wherein in the case that theresidual trigger time is shorter than the inter-frame time interval, itis determined to trigger the CE-MRA scan when the residual trigger timeelapses, and the residual trigger time is calculated and corrected frameby frame.
 13. A method for determining a trigger timing of a ContrastEnhanced Magnetic Resonance Angiography (CE-MRA) scan, comprising:acquiring a blood flow velocity of a target vessel; and determining thetrigger timing for performing the CE-MAR scan on a CE-MRA scan regionaccording to the blood flow velocity and a predetermined imageacquisition condition during a monitoring scan.